feat(cas): content-addressed artifact store (steps 1–8)

New core:artifacts-store interface + infrastructure/artifacts-cas
implementation: segment files + SQLite index, Blake3 hashing,
group-commit fsync via flushBefore, recovery tail-scan, manual
compactor, and oldest-first disk-cap evictor.

Inference events now carry promptArtifactId / responseArtifactId;
orchestrators put bytes before emitting. SqliteEventStore wraps
its txn in artifactStore.flushBefore so segment data is fsynced
before the event commit, making the crash window non-corrupting
(TailScanner re-indexes orphan tail records on reopen).

Compactor and evictor are mutually exclusive via maintenanceMutex.
Step 9 (cloud sync) deferred to a later epic.

See docs/reviews/2026-05-18-cas-steps-1-8-review.md for the final
review.

testing/contracts/build.gradle

@@ -17,7 +17,9 @@ dependencies {
     testImplementation(project(":core:context"))
     testFixturesImplementation(project(":core:events"))
     testFixturesImplementation(project(":core:sessions"))
+    testFixturesImplementation(project(":core:artifacts-store"))
     testFixturesImplementation(project(":testing:fixtures"))
     testFixturesImplementation "org.jetbrains.kotlinx:kotlinx-datetime:$kotlinx_datetime_version"
     testFixturesImplementation "org.junit.jupiter:junit-jupiter:$junit_version"
+    testFixturesImplementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$kotlinx_coroutines_version"
 }

testing/contracts/src/testFixtures/kotlin/com/correx/testing/contracts/fixtures/artifactstore/NoopArtifactStore.kt

@@ -0,0 +1,11 @@
+package com.correx.testing.contracts.fixtures.artifactstore
+
+import com.correx.core.artifactstore.ArtifactStore
+import com.correx.core.events.types.ArtifactId
+import com.correx.core.utils.TypeId
+
+class NoopArtifactStore : ArtifactStore {
+    override suspend fun put(bytes: ByteArray): ArtifactId = TypeId("00".repeat(32))
+    override suspend fun get(id: ArtifactId): ByteArray? = null
+    override suspend fun flushBefore(commit: suspend () -> Unit) { commit() }
+}

testing/contracts/src/testFixtures/kotlin/com/correx/testing/contracts/fixtures/events/store/EventStoreContractTest.kt

@@ -5,6 +5,7 @@ import com.correx.core.events.types.EventId
 import com.correx.core.events.types.SessionId
 import com.correx.testing.contracts.utils.ConcurrencyRunner
 import com.correx.testing.fixtures.EventFixtures
+import kotlinx.coroutines.runBlocking
 import org.junit.jupiter.api.Assertions
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.assertThrows
@@ -13,7 +14,7 @@ abstract class EventStoreContractTest {
     protected abstract fun store(): EventStore
 
     @Test
-    fun `appends preserve ordering`() {
+    fun `appends preserve ordering`(): Unit = runBlocking {
         val store = store()
 
         store.append(EventFixtures.newEvent(EventId("e1"), SessionId("s1")))
@@ -27,19 +28,19 @@ abstract class EventStoreContractTest {
     }
 
     @Test
-    fun `idempotency prevents duplicates`() {
+    fun `idempotency prevents duplicates`(): Unit = runBlocking {
         val store = store()
         val e = EventFixtures.newEvent(EventId("dup"), SessionId("s1"))
 
         store.append(e)
         assertThrows<Exception> {
-            store.append(e)
+            runBlocking { store.append(e) }
         }
         Assertions.assertEquals(1, store.read(SessionId("s1")).size)
     }
 
     @Test
-    fun `sessions are isolated`() {
+    fun `sessions are isolated`(): Unit = runBlocking {
         val store = store()
 
         store.append(EventFixtures.newEvent(EventId("a"), SessionId("s1")))
@@ -50,7 +51,7 @@ abstract class EventStoreContractTest {
     }
 
     @Test
-    fun `readFrom respects sequence cursor`() {
+    fun `readFrom respects sequence cursor`(): Unit = runBlocking {
         val store = store()
 
         store.append(EventFixtures.newEvent(EventId("1"), SessionId("s1")))
@@ -67,9 +68,11 @@ abstract class EventStoreContractTest {
         val store = store()
 
         ConcurrencyRunner.run(20, 100) { t, i ->
-            store.append(
-                EventFixtures.newEvent(EventId("e-$i-$t"), SessionId("s1"))
-            )
+            runBlocking {
+                store.append(
+                    EventFixtures.newEvent(EventId("e-$i-$t"), SessionId("s1"))
+                )
+            }
         }
 
         val all = store.read(SessionId("s1"))
@@ -80,7 +83,7 @@ abstract class EventStoreContractTest {
     }
 
     @Test
-    fun `sequences are strictly increasing per session`() {
+    fun `sequences are strictly increasing per session`(): Unit = runBlocking {
         val store = store()
 
         repeat(100) {
@@ -95,7 +98,7 @@ abstract class EventStoreContractTest {
     }
 
     @Test
-    fun `sequences are isolated per session`() {
+    fun `sequences are isolated per session`(): Unit = runBlocking {
         val store = store()
 
         repeat(50) {
@@ -111,7 +114,7 @@ abstract class EventStoreContractTest {
     }
 
     @Test
-    fun `appendAll is atomic per session`() {
+    fun `appendAll is atomic per session`(): Unit = runBlocking {
         val store = store()
 
         val batch = (1..50).map {
@@ -133,12 +136,14 @@ abstract class EventStoreContractTest {
         val store = store()
 
         ConcurrencyRunner.run(10, 50) { t, i ->
-            if (i % 2 == 0) {
-                store.append(EventFixtures.newEvent(EventId("a-$t-$i"), SessionId("s1")))
-            } else {
-                store.appendAll(
-                    listOf(EventFixtures.newEvent(EventId("b-$t-$i"), SessionId("s1")))
-                )
+            runBlocking {
+                if (i % 2 == 0) {
+                    store.append(EventFixtures.newEvent(EventId("a-$t-$i"), SessionId("s1")))
+                } else {
+                    store.appendAll(
+                        listOf(EventFixtures.newEvent(EventId("b-$t-$i"), SessionId("s1")))
+                    )
+                }
             }
         }
 
@@ -150,7 +155,7 @@ abstract class EventStoreContractTest {
     }
 
     @Test
-    fun `read returns stable snapshot`() {
+    fun `read returns stable snapshot`(): Unit = runBlocking {
         val store = store()
 
         repeat(100) {
@@ -164,7 +169,7 @@ abstract class EventStoreContractTest {
     }
 
     @Test
-    fun `readFrom behaves like streaming cursor`() {
+    fun `readFrom behaves like streaming cursor`(): Unit = runBlocking {
         val store = store()
 
         repeat(10) {
@@ -177,4 +182,4 @@ abstract class EventStoreContractTest {
         Assertions.assertTrue(first.all { it.sequence > 3 })
         Assertions.assertTrue(second.all { it.sequence > 7 })
     }
-}
+}

testing/contracts/src/testFixtures/kotlin/com/correx/testing/contracts/fixtures/projections/ReplayContractTest.kt

@@ -5,6 +5,7 @@ import com.correx.core.events.types.EventId
 import com.correx.core.events.types.SessionId
 import com.correx.core.sessions.projections.replay.EventReplayer
 import com.correx.testing.fixtures.EventFixtures.newEvent
+import kotlinx.coroutines.runBlocking
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Test
 
@@ -17,7 +18,7 @@ abstract class ReplayContractTest<S> {
     ): EventReplayer<S>
 
     @Test
-    fun `rebuild is deterministic`() {
+    fun `rebuild is deterministic`(): Unit = runBlocking {
         val store = store()
 
         repeat(50) {

testing/contracts/src/testFixtures/kotlin/com/correx/testing/contracts/fixtures/projections/SessionReplayContractTest.kt

@@ -6,6 +6,7 @@ import com.correx.core.events.types.SessionId
 import com.correx.core.sessions.SessionCounterState
 import com.correx.core.sessions.projections.replay.EventReplayer
 import com.correx.testing.fixtures.EventFixtures.newEvent
+import kotlinx.coroutines.runBlocking
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Test
 
@@ -18,7 +19,7 @@ abstract class SessionReplayContractTest {
     ): EventReplayer<SessionCounterState>
 
     @Test
-    fun `rebuild is deterministic`() {
+    fun `rebuild is deterministic`(): Unit = runBlocking {
         val store = store()
 
         repeat(50) {
@@ -34,7 +35,7 @@ abstract class SessionReplayContractTest {
     }
 
     @Test
-    fun `rebuild reflects complete stream`() {
+    fun `rebuild reflects complete stream`(): Unit = runBlocking {
         val store = store()
 
         repeat(42) {